Earth Materials. Module 06Earth Materials. Module 06

In this module you should study:

The uses of Limestone as a building material and as a raw material for making other useful materials.

The formation of Crude Oil and how it is processed to produce a range of useful materials, including Plastics via Polymerisation.

How the Atmosphere of the Earth formed and developed

How the Earth’s landscape is changing as a result of the Rock cycle and Tectonic Plate movement

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Limestone is a commonly occurring rock which can be used not only for building, but also for making many other useful materials including Lime, Cement and Glass. It is also added to Bread and Toothpaste.

Limestone is mainly a chemical compound called

Calcium Carbonate CaCO3

Limestone is a sedimentary rock, formed from the bones and shells of sea creatures living millions of yeas ago.

Limestone

Limestone is quarried, then ground up into smaller pieces

Quarrying does however have environmental impacts

Carbonates generally can neutralise acids, so powdered limestone may be used without any more processing, to neutralise the acidity of lakes and soil

Adding too much Limestone will not cause too much damage to the environment. Also it does not get washed out by heavy rain as an alkali would.

Acid + Carbonate Salt + Water +Carbon Dioxide

Carbonates generally break down when they are heated. This is called Thermal DecompositionThermal Decomposition.

Limestone heated in a Kiln undergoes Thermal Decomposition to form Quicklime Calcium Oxide CaO

Calcium Carbonate Calcium Oxide + Carbon Dioxide

CaCO3 CaO + CO2

Thermal Decomposition

QuicklimeLimestone

Quicklime is a very strong alkali, which reacts with water to produce Slaked Lime Calcium Hydroxide Ca(OH)2 (Lime water), this is also an alkali used to reduce acidity in soil.

Calcium Oxide + Water Calcium Hydroxide

CaO + H20 Ca(OH)2Quicklime Slaked Lime (Lime Water)

If you breath into Lime water, it goes milky because the Carbon Dioxide in your breath produces INSOLUBLE Calcium Carbonate, but if you continue to breath into it, the solution will go clear again because the Calcium Carbonate reacts with more Carbon Dioxide and Water to form SOLUBLE Calcium Hydrogen Carbonate.

(This will become more important when we consider changes to the atmosphere).

So, We can think of it like a cycle:

Limestone Breaks down when heated, to form Quicklime, but this reacts with water to form Slaked lime. Slaked lime in turn will react with Carbon Dioxide to form Limestone again.

Reminder:

CaCO3 CaO + CO2

Thermal Decomposition

QuicklimeLimestone

Calcium Carbonate Calcium Oxide + Carbon Dioxide

Calcium Oxide + Water Calcium Hydroxide

CaO + H20 Ca(OH)2Quicklime Slaked Lime (Lime Water)

Calcium Hydroxide + Carbon Dioxide Calcium Carbonate

Ca(OH)2 + CO2 CaCO3

Calcium Carbonate +Water + Carbon Dioxide Calcium Hydrogen Carbonate

CaCO3 + H2O + CO2 Ca(HCO3)2

CementCement

Cement is produced by heating powdered limestone and clay, in a Rotary Kiln

ConcreteConcrete

This is made by mixing together: Cement, Sand, Rock chippings and water. The mixture sets quickly, then hardens slowly producing rock-like concrete.

GlassGlass

There are many different types of glass, each with its own properties and uses, but essentially, Glass is made by heating together a mixture of:

Powdered Limestone

Sand

Soda

(Sodium Carbonate.) Bath Salts

How can so many useful products

be made from Crude OilCrude Oil?

What should we remember from Key Stage 3?

Crude oil is obtained from the Earth’s crust.

It was formed from the remains of organisms which lived millions of years ago.

It is a fossil fuel.

The fossil fuels coal, oil and natural gas have resulted from the action of heat and pressure over millions of years, in the absence of air, on material from animals and plants (organic material) which has been covered by layers of sedimentary rock. (Syllabus statement)

Like all fossil fuels, Crude Oil was formed millions of years ago.

Tiny Sea creature and plants died and were buried on the ocean floor. Over time they became covered with layers of silt and mud. All the Oxygen which would have caused them to rot was squeezed out.

Over millions of years, the remains were buried deeper and deeper. The enormous heat and pressure turned the organic material in their remains into Crude Oil and Methane (Natural Gas)

Today, the Crude Oil lies covered by layers of sedimentary rock. We have to drill down through the rock to reach rock formations which contain Oil and Gas deposits. They occur in bands of porous (spongy) rock.

The Oil is often found in porous rock

Sometimes it is visible in bands of shale

To get it out, we have to drill down into the Earth’s crust

Often the drilling rigs are located miles offshore, on drilling platforms.

The United Kingdom drills for Oil in ‘Oil fields’ beneath the North Sea

We ‘Share’ the Oil field with others in Europe, having a claim to the fields

Oil platforms in the North Sea are huge

They stand on tall legs anchored to the sea bed

Crude oil is a mixture of compounds.

The compounds are mainly made up of the Elements:

Carbon (C)

and

Hydrogen (H)They are referred to as Hydrocarbons

The Chemical and Physical properties of Hydrocarbon Molecules in the mixture are unchanged by the fact that they are in a mixture:

This means that each compound in the mixture will boils at its own, unique, boiling point.

This helps us to separate the mixture

Since it is a mixture, crude Oil found in one location may be different to that found in another.

Hydrocarbons are made up of the elements Carbon and Hydrogen only

Carbon atoms have four electrons in their outer energy level which they use to form bonds with.

This means that they can make four covalent bonds with other things.

C

Covalent bonds are made by sharing electrons with other atoms

C

H

H

HH

They can form bonds with Hydrogen atoms, by sharing electrons.

C

HH

H

H

This diagram represents the hydrocarbon molecule Methane CH4. You will know it as Natural Gas

C HH

H

HStructural formula

Carbon atoms can also form covalent bonds to other Carbon atoms, forming ‘Carbon chains’

CH

H

H

C

H

H

This would represent a molecule of the Hydrocarbon Ethane,

formula C2H6

H

How would molecules of Propane C3H8 and Butane C4H10 be drawn?

Carbon atoms form the ‘Spine’ of Hydrocarbon molecules.

The Hydrocarbons in Crude Oil are made up of single bonds only. They are said to be Saturated Hydrocarbons, because there are no spare bonds for any more Hydrogen atoms.

We call this family of Hydrocarbons Alkanes, they have the General Formula: Cn H(2n+2). E.g. Pentane: C5H12

The number of carbon atoms in the Hydrocarbon molecules in Crude Oil varies from 1carbon to over 70 carbons atoms.

The number of atoms present affects the boiling point of the compound.

This means that each molecule has a different boiling point.

The molecules with the least number of carbon atoms in them have the lowest boiling point.

Methane CH4 Boiling Point = - 163 Celsius

Ethane C2H6 Boiling Point = - 87 Celsius

Propane C3H8 Boiling Point = - 43 Celsius

Butane C4H10 Boiling Point = - 0.5 Celsius

Methane = -163

Ethane = - 87

Propane = - 43

Butane = - 0.5

The boiling point increases as the length of the carbon chain gets bigger.

Having different boiling points means that the molecules can be separated into simpler mixtures by:

Fractional Distillation.

Reminder!Distillation is a separation technique using the fact that different compounds boil at different temperatures (they have different boiling points.) Remember separating pure

water from Inky water in year 7?

When a mixture of different compounds is heated, the ones with the lowest boiling point will evaporate first.

Later vapour is condensed back into liquid.

There are many Hydrocarbon compounds in Crude Oil and this complex mixture is separated into a simpler mixture.

This simper mixture is made up of Fractions, groups of Hydrocarbons with similar carbon chain lengths.

The Crude Oil is first heated to make it Evaporate, then it is allowed to cool at different temperatures, so that different Fractions Condense at different points.

This process is called Fractional Distillation.

Hot Crude Oil in

LPG for calor gas stoves

Petrol for fuel

Naphtha for chemicals

Paraffin for aeroplanes

Diesel for Fuel

Fuel Oil for heating

Bitumen for Roads

Lubricating Oil for machines

350OC

40OC

Temperature decreasing

Average carbon atoms = 3

Average carbon atoms = 8

Average carbon atoms = 10

Average carbon atoms = 12

Average carbon atoms = 20

Average carbon atoms = 40

Average carbon atoms = 80

Average carbon atoms = 120

The larger the molecule,

(the more Carbons atoms there are) :

The more Viscous it is (the less easily it flows).

The less easily it ignites (the less Flammable it is).

The less Volatile it is (the harder it is to turn from a liquid into a vapour).

The higher its Boiling Point is.

All these points mean that large Hydrocarbons are less use as fuels than smaller Hydrocarbons.

Since shorter molecules release energy quicker by burning, there is a greater demand for shorter molecules than for longer ones.

Longer molecules are broken down or Cracked into shorter, more useful ones.

The process is called Catalytic Cracking.

The hot Hydrocarbons are vaporised and passed over a hot Catalyst. A Thermal Decomposition reaction occurs. The products contain some molecules which are useful as fuels and some which are useful to make plastics from.

More about Catalytic Cracking

Cracking involves breaking a bond between two carbon Atoms. The ‘free’ ends of the broken bonds are very unstable, so the two new molecules rearrange themselves.

One ‘free’ end picks up a hydrogen atom to make an Alkane, the other joins onto the next carbon atom to make a carbon-carbon double bond, to form an Alkene.

Cracking

C10H22

a Saturated Alkane

C2H4

an Unsaturated Alkene

A Test for Unsaturated Hydrocarbons

The Carbon - Carbon double bond is very reactive. Some molecules like Bromine, can be added across the double bond

Bromine water added to an Alkene,will go from yellow - orange to colourless, as the Bromine reacts with one of the Carbon - Carbon bonds.

Why bother about Alkenes?

The double bond in Alkenes makes them very reactive.

Alkene molecules can be added together to form longer molecules called Polymers.

The process is called POLYMERISATION.

Why bother to cut hydrocarbons up, just to stick them back together again?

Choosing the right Alkene allows us to ‘tailor make’ the polymer with just the properties we need. Plastics are polymers.

Addition Polymerisation

Molecules of Alkenes are referred to as Monomer molecules. If they are added together, with no other compounds being involved, the process is called Addition Polymerisation.

E.g. Polymerising ETHENE to make Poly(ethene) Polythene.

Ethene to Poly(ethene)

Representing Polymerisation

For any addition polymerisation, the way to represent it is basically the same.

For ‘n’

(any number) of monomer molecules.

The repeating unit will be repeated ‘n’ number of times

E.g. The polymerisation of Ethane C2H4 :

H H

H

H H

HH H

Monomer

Ethene

Unsaturated hydrocarbon

Polymer

Poly(ethene)

Good for plastic bags & buckets etc..

H H

H

H H

HCH3 CH3

E.g. The polymerisation of Propene C3H6 :

Monomer

Propene

Unsaturated hydrocarbon

Polymer

Poly(propene)

Good for ropes etc..

H H

H

H H

HC6H5 C6H5

E.g. The polymerisation of Styrene :

Styrene Monomer

Poly(styrene)

Polymer

Packaging, foam cups etc.

H H

H

H H

HCl Cl

E.g. The polymerisation of Vinyl Chloride :

Vinyl Chloride

Monomer

Poly(vinylchloride) PVC

Polymer

Window frames, waterproof clothing etc..

E.g. The polymerisation of Tetrafluroethene :

F F

F

F F

F F F

Poly(tetrafluroethene) PTFE

(Non-stick coating - Teflon)

Polymer

Tetrafluroethene

Monomer

Monomer Polymer Typical uses

Ethene Poly(ethene) Plastic bags,buckets

Propene Poly(propene) Rope & string

Vinyl Acetate Poly(vinylacetate)PVA

Wood glue

Styrene Poly(styrene) Cups, insulationPackaging

Some uses of Plastics

Problems with Plastics

The co-valent bonds holding the long molecules together are very strong. Few bacteria can make them rot down. They tend not to be Biodegradable.(What does this word mean?) This makes disposing of plastics difficult:

Burning them produces oxides of Carbon, Hydrogen and sometimes Sulphur and other toxic compounds:Carbon Dioxide, Sulphur Dioxide, Water vapour

They fill up land-fill sites.

(Why should these factors be a problem?)

Recycling plastics is complicated by several issues: Not all plastics lend themselves to recycling

Different types of plastic have different properties, and so separation is very important.

The economics of recycling are not always favourable, as the market is prone to fluctuate. For example, when oil prices fall the production of ‘new’ plastics become cheaper, so providing its recycled counterpart with greater competition.

Unlike some countries a lack of subsidy in the UK makes a recycling industry more difficult to sustain, so nationally our recycling performance tends to lag behind many of our European neighbours.

However, increasing pressures on landfill sites, and our need to conserve natural resources makes recycling of plastics an important step forwards.

Why not recycle plastics?

Waste to Energy Process (WEP)

In instances where there is a high proportion of thermosetting plastic, or the waste is highly contaminated such as in the domestic waste stream, the best use of resources may be to burn the plastic waste and using the energy to generate heat and power.

Plastics have a high-energy content, so although they are roughly only 10% of household waste they contain over 30% of the energy content

In modern WTE plants the combustion process is highly controlled and combined with extensive air pollution and ash management systems.  This enables the process to comply with government regulations for air, water and solid waste emissions.

Why not burn them then?

The need for a balanced solution

Plastics are clogging up land-fill sites and incinerating them adds to green-house gases and produces toxic gases: Ban plastic packaging and force supermarkets to revert to paper bags and glass bottles etc..

Plastics come from a valuable resource. Most plastic products have their type stamped on them (e.g.. ABS), get councils to force residents into recycling different types of plastics in different bins.

Plastics are mainly hydrocarbons like fossil fuels. We burn fossil fuels in power stations, so just burn plastics instead, being careful to scrub the fumes. This will save some fossil fuels and generate electricity at the same time.

Investigate the economics: To make 1000 glass bottles from raw materials takes the equivalent of 230kg Oil, making 1000 plastic bottles takes just 100kg.

To make 1000 paper bags takes 47kg Oil, to make 1000 plastic bags takes just 32kg. Using plastic uses less Oil, doing less damage.